1. Field of the Invention
The present invention relates to an optical scanning device, and an image forming apparatus on which a polygon scanner and an optical element are installed.
2. Description of the Related Art
In an optical scanning device that performs optical writing onto a photosensitive element (image carrier) of an image forming apparatus, a light beam is deviated from an optical axis due to ambient temperature change over time. Therefore, an irradiation position of the light beam onto a surface to be scanned on the photosensitive element is changed. This causes image defects such as color shift in a tandem color machine or the like in some cases. In order to solve the problem, various scanning line adjusting units and configurations of an optical housing that is hard to be affected by thermal deformation have been conventionally proposed.
However, a known optical scanning device including a scanning line adjusting unit requires an adjustment mechanism for automatically adjusting a scanning line when color shift occurs over time as described in Japanese Patent Application Laid-open No. 2006-259408, for example. Such automatic adjustment is performed as follows. An adjustment trigger is provided during continuous printing; and an adjustment time for automatically adjusting a scanning line under predetermined conditions is set. Furthermore, a color shift amount is measured at this time so that color matching is performed by the scanning line adjusting unit. Accordingly, the automatic adjustment has significant disadvantages in that a waiting time required for a user increases or toner is used in the control for measuring a color shift amount, for example.
In addition, Japanese Patent Application Laid-open No. 2009-198888 discloses an optical scanning device having the following configuration in order to reduce color shift or color unevenness caused by distortion of an optical housing due to ambient temperature change over time. In the optical scanning device disclosed in Japanese Patent Application Laid-open No. 2009-198888, holes (openings) are provided at bases of ribs, the ribs being provided in a standing manner so as to be opposed to each other around a polygon scanner serving as a heat source arranged inside of the optical housing.
However, the configuration of a resin molded article such as an optical housing is complicated, and therefore, a thermal deformation state of such article has a complicated deformation mode in most cases. Therefore, simply providing holes around ribs that are opposed to each other near the polygon scanner can reduce a thermal deformation amount of the optical housing, but may adversely affect attachment postures of various optical elements such as lenses. Therefore, the problem of defective images generated over time, such as a color-shifted image, remains unsolved.
An object of the invention is to solve the problem that image defects occur due to temperature change over time in some cases in the conventional optical housings and is to provide an optical housing, an optical scanning device, and an image forming apparatus that can suppress the occurrence of defective images such as color-shifted images due to temperature change over time without using a scanning line adjusting unit.